Microsoft Office 2016 is compatible with your Mac and with High Sierra. However Microsoft ended support for Office 2016 over a year ago and finding a copy to buy may be difficult. Some years ago, I had Office 2011 on a Macbook Air 2010 running High Sierra and upgraded it to Office 2016. The 2016 version had additional features and some bug fixes, but I don't recall it being faster.
To go from Office 2011 to Office 2016 requires purchase of the new version of Office 2016 (if you can find it). Its is not a free update or upgrade, it is an entirely new version.
How much memory and free disk space do you have?