SQL Server Difference between CPU and CPU_TIME
Here's what I can tell you. 

Internally, they use two different ways obtaining the data; sysprocesses uses the "legacy" method and sys.dm_exec_requests uses a newer method. Unless you have a very pedestrian workload these will generally not be the same.

Overall, I must agree with Aaron and not use sysprocesses as it is deprecated. Having said that, either method will get you "close enough" to troubleshoot issues and there shouldn't be such a difference that it hides or masks an issue from your troubleshooting efforts.

Note, this was tagged as SQL2014 and thus this answer should be considered relevant only for SQL Server 2014 specifically build 12.00.5538 (SP2 CU3).