Can I use both Thunderbolt ports to get higher resolution/framerate
The problem is not the speed of the connection, a Thunderbolt 2 port has the bandwidth for a display size and refresh rate of at least 4K@60Hz or 5K@30Hz.  Using two Thunderbolt connections to a single display requires a display that supports this, and this is a feature that I recall was short lived as there are now cable and connector standards readily available for supporting 8K displays with refresh rates of at least 60Hz.
The problem is not a lack of bandwidth.  The problem is that the GPU in the laptop doesn't support more than 4K@30Hz.  To get better than this means adding an external GPU, or getting a new computer.