This app was mentioned in 3 comments, with an average of 2.33 upvotes
https://play.google.com/store/apps/details?id=com.synprez.fm&hl=en_US
or even better:
https://play.google.com/store/apps/details?id=com.rockrelay.synth.dx7.piano&hl=en_US
Compatible with DX7 patches!!!
WebApps are just websites accessed via Chrome. Android apps are installed from the Play Store, which you must have just done if you installed DRC.
OK, try SynprezFM. This is about as basic as you can get. If you can't run this without lag, then you probably can't run anything, I'm afraid.
What processor does your chromebook have, and how much memory?
Also, if you haven't already tried, plug just one midi device directly into your chromebook (no usb hubs), and play the audio directly from your chromebook's speakers. (Just in case the lag is coming from somewhere else.)
I don't know Android audio apps at all. This one appears to be SynprezFM II
Sunvox and Caustic 3 are often recommended