Force refresh of Preview

FWIW, I tried a PDF 171 page manual and several large RAW photos and zoomed and scanned and whatever else I could think of. The most memory Preview was using was about 400MBs.

You might want to change your profile, it still says you are running Yosemite.

I see. The 171 page PDF manual I tried has text and graphics and was 7.4MB. The RAW image file was 34.4MB, 7360 x 4912. Something you have installed may be causing a problem.

Please install and paste the results

http://etrecheck.com/

The largest architectural drawings I happen to have are about 40 MB in size and several feet long. Sometimes, Preview has a hard time manipulating them, but it's only intermittently unresponsive and I can't really make it totally fail in the manner you describe. During that time, Preview's memory usage is not particularly significant.

If Activity Monitor's unitless "Memory Pressure" graph never becomes "red" then the problem is not a memory limitation. I'd still quit the other apps you are using in an effort to advance troubleshooting. "Parallels" in particular is using a lot of it.

That's not to say that Preview itself is perfect, and it may simply be having trouble with those drawings. It is possible there is something odd about the way they are coded. Open an example of one that has been giving you trouble, then choose Tools > Show Inspector and choose the General Info pane (leftmost icon).

Capture a screenshot of that window and post it in a reply. If it contains confidential information, obscure it before posting.

Sounds like a possible memory issue. Open Activity Monitor and check how much memory Preview is using.

When you say large PDFs, how large? I haven't run into an issue but mine might not be large enough. If there is no confidential info can you post one somewhere?

Could you re-run Etrecheck test, and post the results?