Don't know what you did, but this is how the 1.15 (and all of its snapshots) run for me: https://imgur.com/a/qhkbdsI
For the record, I can hit 60fps in 1.14.4 almost constantly. In the world I've did this screenshot on, I have no heavy redstone machinery (in fact, none at all as I didn't get to that point yet), just a starter house (slab of dirt with bed, crafting table and furnace inside). I blame Blaze3d.
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violine1101
wobst.michael
Plus CPU is extremely weak and below minimum requirements.
migrated
Why should hardware specs depend? The performance is still lower than before.
Your graphics card doesn't seem to be powerful enough to handle a render distance of 12 chunks.