Cricket will not activate a Sprint Device onto their network. Sprint runs on CDMA technology and it is incompatible with Cricket that uses AT&T's GSM towers.
Unfortunately, Sprint devices will only run on Sprint or a Sprint mvno. Check the lists here: https://en.wikipedia.org/wiki/List_o...work_operators and see which ones might activate your device. Even they might want you to get a new phone to use their service. I've not really heard on anyone activating Sprint onto an mvno, although it might happen. Basically I don't hear much about Sprint mvnos and it is an area I like to keep informed about.
If it is for signal reasons, you will have to get a new phone to take advantage of Cricket. Any Cricket Branded phone will work, any AT&T branded phone will work, even without an unlock. Any GSM unlocked phone will work if it has 3G 950/1900 and LTE bands 2/4/17 on the radio.
If it is just to save money. Shop a bit harder and consider service + phone in your calculations.