Before I begin, my system specifications are Ryzen r7 2700, 16gb RAM and RTX 2060, very capable hardware.

To begin, I've run some "at home" tests between Minecraft Java 1.14.4 and 1.15.2. For my tests I generated a world in 1.14.4, then copied the world. After copying the world I launched two clients, one running 1.14.4 and the other 1.15.2. First loading up the world is roughly the same with the first big chunk load dipping fps for a couple seconds then it jumping up. My 1.14.4 client once stabilized, sitting still is roughly 250-300 fps. Not too bad. I move around and start to load and unload chunks, and it stays between 100-150, still very playable. Next I put on a well known 128x resource pack (Chroma Hills). Results roughly the same, maybe 5-10% less fps across the board. All 1.14 tests stable and playable, also for reference 16 chunk render distance with maxed out graphics settings was used for this aside from biome blend which I kept at the stock 5x5. Now on to 1.15, same world standing in exact same spot, staring at exact same block, idle fps is somewhere around 175-200. That's reasonable, still pretty good. When I start to move and load and unload chunks, I'm now dipping to about 70-100. That's a pretty large drop and still playable, but whether it was 70 or 100 fps there was stuttering, not horrendous unplayable stuttering, but enough stuttering to definitely make the experience much less enjoyable. Moving on to resource pack test, same resource pack at 128x and it's a much different story, 120fps max at idle and moving around is 40-80 and now the stuttering is much worse and comes with lag spikes.

Now, I understand there were chunk rendering improvements made for servers in the newest full release that is supposed to help servers, specifically ones with high amounts of players in a single world. I also understand using a resource pack isn't a necessity to enjoy the game, although it certainly heightens the experience by being able to play Minecraft in higher resolutions. But, I'm really curious why I'm seeing such degraded performance client side when running 16 chunks if not 24 chunks has never been an issue. Even including higher resolution resource packs. I'm more or less trying to see if maybe there's something config wise that could help resolve this or if I'm more or less just forced to reduce my render distance from here on out. This game is incredibly fun and being able to play it at high fps and with good resource packs is why I and many other people have invested in decent computers(and other games of course).

The included picture is with the resource pack on both clients with the proper version of it.