Optimize Gradle Compilation Speed for Online Compiler Service

Project:
I run an online Minecraft plugin compiler. Currently using javac for everything because fresh Gradle starts take 40-100+ seconds. Need someone to get Gradle compilation under 10-15 seconds while maintaining security.

Current Setup:
Each compilation runs in isolated Docker container (no network, read-only FS)
Cannot reuse Gradle daemons between compilations (security - running untrusted code)
Compilation service runs on same server as main API
Need full Gradle support (multi-module, custom tasks, dependency resolution)

Problem:
Gradle cold start is too slow for web service
Currently forcing everything through javac which breaks complex projects
Need <15 second Gradle builds regardless of project size

Requirements:
Make Gradle fast without compromising security
Must handle untrusted code safely
Full build.gradle parsing and execution
Solution that works on single dedicated server

Deliverables:
Working implementation
Security documentation
Performance proof (<15s for Gradle builds)