When launching Minecraft Java 1.15.2, there is the small pull-down/up window near the bottom left. I have to choose either Optifine or Forge. Can I run both of these at once so I can have my mods and great graphics?
Select the Forge profile and place Optifine in your mods folder like any other mod. Optifine can be installed to be used by itself or as a mod to use along with Forge. The latest preview version of Optifine for 1.15.2 can be used with Forge 31.1.63 (download link here).
That mod was only necessary before Optifine's 1.15.2 preview versions had built-in support for Forge. You no longer need Optiforge now as the latest preview build already supports Forge 31.1.63 like I mentioned above.