I used to be on 15 mg of adderall instant release 3 times a day. As of yesterday i was prescribed to 10 mg of adderall XR two times daily. Come to find out that the pill that i heard could last up to 12 hours only last 6 for me. My next appointment with my doctor is friday so i have to just wait out until then, but i have a huge test on this wednesday and i dont feel that the XR is working at all. My doctor wants me to keep taking the XR until we meet again.

My question is,
1) Can i take an instant release pill after i feel the XR one wear off?

2) On the day of my test would it be unsafe to skip the instant release pill all together for just one day to take just the instant release kind, (which remember is a higher dose of 15mg) and go back to the XR the next day.

so basically can you switch the type of pill?

Thank you for your help and time!