Regarding the first issue, please take a look at our knowledgebase article on how to optimize your computer for working with a DAW.
You can find it here .
Another thing you should check is the buffer size you have selected.
You can find an explanation regarding this in the UR22's operation manuel on page 8.
Regarding you second issue, please be aware that the output on the rear of the UR22 are Line outputs, which ARE mono. Therefore you find two of them. One is called 1/L (for left), one is called 2/R (for right).
If you want to connect your headphones to the UR22, please use the phones socket on the front panel.
You can find an explanation of the connection setup of the UR22 on page 10 in the operation manual.