2015 Mac takes 5 min to load up??

Another thing to try is reinstalling Mac OS from the Recovery Partition. This will put back in place any missing or damaged portions of Mac OS and will not affect your data or applicatons. However, that being said it is extremely wise to ALWAYS have a complete backup of your system prior to doing this for insurance. How you do the re-install is to boot into the Recovery Partition (Command + R on startup) and then select Install Mac OS and install on the same drive it is currently installed on. Then re-start to re-test.

If you do get to a point where you need to replace the drive, please take it to an Apple Authorized Service Provider for them to do the work. It is definitely money well spent.

Did you restart in Safe Mode as advised? This would clear any caches that may have become corrupted and may help.

Also, I see your system still only has 8GB of RAM installed, this is considered the bare minimum to run Mac OS. You may want to consider upgrading to 16GB or more. If you have a lot of startup items selected each of these require RAM to start and may be competing with one another for any available RAM, this could cause slow startup times.

If you decide to upgrade the RAM, please only use Crucial.com or www.macsales.com RAM. Why these 2 vendors, easy iMacs are sensitive to using quality RAM. Both vendors supply high quality products, have competitive pricing, offer great service and well they just work. Buying "value" RAM is a waste of time and often causes failures. If you are in the US, select either vendor. If you are outside the US I'd recommend Crucial so you don't have to pay extra for shipping.

I am pleased the install fixed the problem.

If you upgrade the RAM, please only use Crucial.com or Macsales.com RAM. The reason for recommending these two vendors is iMacs are VERY sensitive to using quality RAM. So-called "value" RAM, has zero value on an iMac and in most cases will fail. Both of the recommended vendors sell very high quality products at reasonable prices and the RAM has a lifetime warranty.

Welcome!

You will find that CleanMyMac will eventually prove detrimental to performance. It has for everyone else.

"Now once I get logged in, the speed of everything is amazing! Zero issues at all."

Does that mean the apps launch fast once the computer has booted? Normally a 5-minute boot time indicates a failing hard drive but that should also slow app launches too. This could be because you have too many things launching at boot in your User Login Items (part of the Users & Groups System Pref).

For now I recommend posting a secure "snapshot" of your system config. Without seeing any private information we can quickly and within the confines of these forums help you determine if software issues are the problem if you use EtreCheck, available free from the Mac App Store here:

https://itunes.apple.com/us/app/etrecheck/id1423715984?mt=12

We can also see hard data about drive performance and RAM usage, allowing us to make a call on whether more RAM would help. EtreCheck is the development of a long-serving and trusted contributor here expressly for displaying information in these forums to help us help you. It will not reveal any personal or secure information.

Run it, select “Report" from the left-hand pane (scroll down to the bottom of that pane to find) and, when its report displays, click the "Share Report" icon from EtreCheck’s toolbar and then "Copy report” from the resulting dropdown.

Please DO NOT highlight the text in the report before using Etrecheck’s “Copy report” command—that will garble the formatting and make the report slower and harder to evaluate.

NOTE: Recent changes to the forum software require you use the “Additional Text" icon (see example below) to embed the report into a post:

Paste the report into the resulting “Additional Text” window:

Also see this excellent user tip on posting text reports like EtreCheck. It is better illustrated than mine.

How to use the Add Text Feature When Post… - Apple Community

In addition to the wise counsel you have already received regarding CMM you also have Symantec Antivirus installed. At best Symantec (and all other third party Antivirus apps) is worthless and will create more harm than good.

Mac OS is extremely secure and does not benefit from or need any third party antivirus, cleaning or ANY third party "maintenance" apps. Mac OS is extremely secure and if simply kept up-to-date and otherwise left alone Mac OS runs securely and quickly for many years. Please locate the Symatec uninstall instructions and uninstall it. Then please restart the computer in Safe Mode per the directions in the link below. Finally, restart normally and chances are good your computer should operate just fine.

https://support.apple.com/en-us/HT201262

Good luck.

No Anti-Virus software or so-called “cleaning” apps are needed or recommended for Mac OS. They can conflict with Mac's own built-in security. At best they will slow your Mac by using unnecessary resources and at worst will bork your entire system.

Symantec and CleanMyMac is a lethal combination. Either one can bring your Mac to its knees and with both running together I'm surprised you're able to use it at all.

Uninstall both as per the developer's instructions and run another Etrecheck report.