Hmm, this is really a last resort solution for me as I really like spotlight and I use it all the time, especially on my other macbook. How come a MacBook Pro from 2012 searches faster than an iMac (greater specs) for 2015! 512 GB on both options.
I sometimes use EasyFind which is pretty good, but both it and "Find Any File" are *non-indexed* searches. They do a blunt, brute-force search, so on large volumes are vastly slower than Spotlight, assuming Spotlight (or indexed Finder search) is working OK.
I'd first suggest you rebuild your Spotlight indexes for each drive (inc'l system volume) using this procedure: https://support.apple.com/en-us/HT201716
This will take a while to rebuild. You can monitor the progress by doing a CMD-space and typing "index". While the job is running it will say "indexing", then when finished it will no longer say that.
Although Spotlight indexing underlies both Spotlight and Finder searches, searching via Spotlight (CMD-space) can also invoke other types of searches such as internet. These can be adjusted via Spotlight Preferences: https://support.apple.com/kb/PH25486?locale=en_US
So after rebuilding Spotlight indexes, if it's still slow your next step is evaluating whether you're searching from Finder (CMD-F) or the Spotlight interface (CMD-space). Searching from Finder should be only your hard drives or maybe network drives. If the search performance varies a lot between these two methods, that could indicate the Spotlight interface has been configured to search more areas, possibly slower storage such as internet. In that case evaluate and adjust the Spotlight preferences.
However even an indexed Finder search might be slow if you're searching a large, slow network drive. Is it possible your 2012 MBP is not searching these, and your iMac is?