I'm not too familiar with Vapor but my first suspicion is that there's a cache somewhere that's having to "warm up" again after each fresh deployment, though you mention that you've already looked into that area. One person on https://www.reddit.com/r/laravel/comments/rgvdvj/laravel_bootstrapping_slow/ mentions PHP's OPcache config settings as a possible culprit (in particular see https://www.reddit.com/r/laravel/comments/rgvdvj/comment/honqsd4/). Maybe something to look into?