obsolete processor

That question can be taken 2 ways:

1. Is a Cortex-A15 likely to be capable of performing a task previously handled by an P89CV51RB2?

Computationally, there is no question - a Cortex-A15 has many orders of magnitude more processing power than any 8051.

In terms of interfacing, it's less likely - a Cortex-A15 really isn't designed or intended for the kind of low-level interfacing tasks where an 8051 shines.
The P89CV51RB2 is a 5V part - you're unlikely to find a 5V Cortex-A15!

etc, etc,...

2. Are you capable of implementing the system on a Cortex-A15?

If you need to ask that question, then the answer is, most likely, "No".

That question can be taken 2 ways:

1. Is a Cortex-A15 likely to be capable of performing a task previously handled by an P89CV51RB2?

Computationally, there is no question - a Cortex-A15 has many orders of magnitude more processing power than any 8051.

In terms of interfacing, it's less likely - a Cortex-A15 really isn't designed or intended for the kind of low-level interfacing tasks where an 8051 shines.
The P89CV51RB2 is a 5V part - you're unlikely to find a 5V Cortex-A15!

etc, etc,...

2. Are you capable of implementing the system on a Cortex-A15?

If you need to ask that question, then the answer is, most likely, "No".