Running a game directly from a compressed .7z file (without extraction) is impossible for emulators. Once you extract to an ISO or JB folder, the game runs at full speed because RPCS3 reads the uncompressed data from your drive.
A popular alternative for faster speeds. Many of its PS3 ISOs come pre-decrypted, which simplifies the process for users who want to "download and play" without extra tools. ps3 games download high quality iso highly compressed work