Yes, the L61 supports up to v20. Keep in mind, you will have to have RSLogix5000 v20 installed, 20.05 preferably. Your PanelView won't notice the difference. What else is in your CLX rack? Most likely, nothing in your CLX rack will care either, I'm always a bit uneasy about ControlNet/DeviceNet, or other specialty cards.
Worth the upgrade? If there isn't something specific you are addressing with the upgrade, then I'd say it probably isn't worth it. I guess Rockwell addressed some security related issues in the newer version of v20, so you can take that into consideration. At the end of the day, your machine is working and producing. Assuming no issues, your machine will still be working and producing after the upgrade. So no gain there. Any hiccups will just be a net negative.
If it ain't broke, don't fix it.
I think RA added little things to v20 software that might make a better experience for users. I think they had tag filtering in the tag database, which they didn't have in v15. Things like that.