MBP 2015 8GB/128GB: Ventura, Sonoma, or stay on Sequoia? Looking for stability/battery.

System Specs:

• Model: MacBook Pro 13" Early 2015 (MacBookPro12,1)
• Processor: 2.7 GHz Dual-Core Intel Core i5
• Memory: 8 GB 1867 MHz DDR3
• Storage: Original 128 GB SSD (Currently 85% full)
• Maintenance: Brand new NinjaBatt battery and fresh thermal paste.

Current Situation: I've tried all three OS, now I'm currently running macOS Sequoia 15.7.2 While it works, I'm noticing significant battery drain and UI lag, especially when doing basic tasks. I really value snappiness so I activated Reduce transparency in settings.

My Workflow: I use the Mac for teaching (iDoceo, Microsoft Suite), watching videos on YouTube/browsing (Arc Browser mainly) and some creative work (CapCut for video, ON1 Photo RAW, and Lightroom for photography).

My big dilemma:

1. For an 8GB RAM / Dual-Core setup, is Ventura significantly smoother than Sonoma?
2. How is the battery life difference between Sonoma and Ventura on this specific model in your experience?
3. Does the 128GB SSD bottleneck Sequoia's performance due to swap files? Should I prioritize a disk upgrade or a downgrade to Ventura?
4. Are there any major bugs in the current OCLP patches for Sonoma/Ventura that I should be aware of? I remember having problems with my airpods pro connectivity back in Sonoma...

Looking for the sweet spot between having a modern OS and actual usability.

Thanks a lot!