MacBook Pro 13in Late 2012 v.s. MacBook 12in Early 2015 I have

MacBook Pro (Retina, 13-inch, Late 2012)
Processor: 2.9 GHz Intel Core i7
Memory: 8 GB 1600 MHz DDR3
Graphics: Intel HD Graphics 4000 1536 MB
Storage: 768GB SSD


I mainly use it for LaTeX, Mathematica and MS Office 2016 for Mac.

I am considering purchasing

MacBook (Retina, 12-inch, Early 2015)
Processor: 1.3 GHz Intel Core M
Memory: 8GB 1600MHz DDR3
Graphics: Intel HD Graphics 5300 1536 MB
Storage: 512GB SSD


or a newer one, if available.

Would it (MacBook, 12-inch) run faster than my MacBook Pro?
According to the specifications you have given, you most likely have a i7 3520M on your MBP and a Core M 5Y71 on the MacBook. If you compare the benchmarks done on the CPUs, you'll see that the i7 excels both on CPU as well as the GPU benchmarks.

Your current MBP is more powerful than the Core M MacBook that you are considering. It will be kind of a downgrade if you purchase it. Wait until WWDC 2016 to see if Apple upgrades it MacBook product line.