Hello,

You have first an internal memory of 16 gigabytes then you decide one day for buying an sd card when it is 15 gigabytes.

1 - sd card doesn't relate to the RAM:

Having one gigabyte of RAM before and after inserting the sd card because it only relates to the space.

This means slow applications before will not be faster after.

2 - Incompatibility or version of android:

By having more spaces of storage you need manually to upgrade the version of your mobile phone because it has nothing to update the version of android.