Use (part of MAME tools) to convert your PS2 ISOs to .CHD format. This is lossless and reduces game sizes by 30-40%.

Technical Approaches and Limitations

: PCSX2 and other emulators can read .gz files directly. Compressing an ISO to GZIP with "Ultra" settings in 7-Zip can significantly lower the footprint. Manual Size Reduction (RIP/Lite Versions)

Finding authentic PS2 games highly compressed to under 50MB is rare because standard PS2 discs range from 700MB (CD-ROM) 8.5GB (DVD9)