TheFinkie

This is a good point: it could be a compatibility issue between Forge and Optifine. However, this is unfortunately very difficult to check. Disabling Optifine causes my FPS to jump wildly between 20 and 120 fps on both Vanilla and Forge. From what I can tell, there isn't a great difference between the average framerate whether Forge is used or not, so that would possibly point to the compatibility between the two being the culprit. If that is the case, I guess I should direct my question at the Optifine developer instead of here. I am still curious to know if this is something other people have encountered, because it's a major issue that must affect 90% of Forge users – unless I have something wrong with my settings, somehow.

I am getting much lower framerates with Forge installed. This is especially noticeable in densely-foliated areas, e.g. Modified Jungle. The issue is only present in Minecraft 1.15+. I checked two versions: 1.15.2 and 1.16.2, and these both displayed the same problem. However, it was not present in 1.14.4. I have tried both the recommended and latest Forge versions. This made no difference. I have NO OTHER MODS installed, except for Optifine. Running exactly the same world without Forge (but still with Optifine) removes the problem. I have BSL shaders on in the screenshots to make the difference more obvious, but the issue is NOT the shader. I still lose a significant amount of frames without shaders on. The same can be said for any other generic FPS fixes (render distance, video settings, etc.). If I am able to run Forge in 1.14.4 and Optifine in 1.15.2, there should be no problem running both in 1.15.2. I tried installing Forge into a new directory and this did not help. The screenshots attached illustrate what I'm saying. NO settings have been changed between them, apart from what's mentioned. Each screenshot is taken several minutes after loading the world. As far as I can tell, the problem MUST be caused by Forge somehow. Is this a known problem? Is there any way I can fix it? Is it a Forge bug or something else? Fig.1: Minecraft 1.14.4 with Optifine – runs perfectly. https://imgur.com/1Lxmwa5 Fig. 2: Minecraft 1.14.4 with Optifine & Forge – runs perfectly. https://imgur.com/HIE1lT1 Fig. 3: Minecraft 1.15.2 with Optifine – runs perfectly. https://imgur.com/EogailO Fig. 4: Minecraft 1.15.2 with Optifine & Forge – huge FPS drop. https://imgur.com/F5cewVl