How to migrate from 13 inch MBP to 15 inch with 13 inch's SSD? I am in this unusual scenario. I have a Mid 2010 13in MacBook Pro and I am trying to make my family's 15inch Mid 2012 MacBook Pro my new personal laptop. However this 15 inch model has a crappy hard disk drive which is beyond slow and makes the laptop unusable for me. How would I migrate to this 15 inch laptop and use the SSD from the 13 inch one? 

What is the most efficient way of going about this? 

Right now, I cannot think of any other solution but to  use Migration Assistant to transfer data from SSD to the HDD in the 15 inch and then taking out the SSD in the 13 inch MBP and cloning it with the HDD that just got all the data from the 13 inch. I am hoping there is a better way than this.
In the past, I have just swapped the drives in the two machines, and everything just worked fine.

Take the SSD from the 13" MBP and put it in the 15" MBP.

In the unlikely event that there are any problems, you can always swap the drives back.

EDIT: You might want to boot into recovery mode, and do a 'Verify Disk' in the Disk Utility, to make sure that everything is fine. As suggested in a comment above, consider a PRAM reset and an SMC reset, to make sure everything is on the same page.