Tbh for me there is no plugin that should cause trouble and there is no that many plugins to drop fps but:
first of all I would check if only basic lspdfr cause similar issue (drag everything from plugins folder to another one created for example at desktop - leave only lspdfr.pdb and lspdfr.dll) - I doubt it will help to solve problem but it won't hurt to check;
update: Gameconfig.xml, HeapAdjuster, Packfile Limit Adjuster;
at OpenInteriors.ini check that you have disabled things that are not recommended;
prob second stupid idea but I would check if with disabled mods game works better (maybe there is smh that start working when you start duty - game adds more ped with smh what drop fps, spawn more modded cars or change AI behavior);
prob third stupid idea: same as above but with scripts;
Let me know if smh have worked (or not worked and then we will try to find another solution)