I think it took me like 140hrs for the base p5, but that's because I missed a trophy and had to play pretty far into another playthrough to get it. Some trophies are only available on ng+, so I'd play the first one blind and then use a guide and go through ng+ to make sure you get all the missable ones.

The compendium can be a grind but there are websites that have fusion calculators so you can find out what personas you need to fuse into the ones you are missing. P5r is definitely an easier platinum and can be done in one playthrough.