This is a generic response for the texture loss forums.
Most of the answers we have all read will help. Disable "Main.PreloadAllModels", change 4K to 2K textures and so on. But the real deal is your texture quality in the GTA V settings. When I run LSPDFR with all emergency vehicles replaced and over 30 add on cars at HIGH texture quality, I face texture loss at maybe 20 minutes in at most. That's 20 minutes if I don't call in back up and make sure EMS and my custom corner van don't over lap.
When I place my texture quality to medium, I can play for hours so long as I don't crash for any reason. Granted, the game doesn't look as nice, and some folks may rather restart every 15 to 20 minutes, but with my PC and my settings, I can play for hours uninterrupted by broken textures. On top of changing texture quality to medium I also keep my distance scaling, population density & variety at 80% or lower which helps my system process everything. All other graphic settings are set to max.
i7-8700K @ 3.7GHz
GEFORCE RTX 2080
32GB RAM (Corsair Vengeance RGB)