There might be a game setting that controls this, if not you'll have to patch 0_master.hkx by adding a custom animation variable that controls the animation playback speed.
First you are going to need to use BSAOpt to unpack the animations BSA. Then you will need hkxcmd.
Extract hkxcmd to the character directory in your unpacked animations BSA. Run the windows command prompt and navigate to the directory which hkxcmd is in. Then type in the command 'hkxcmd convert behaviors'. Now all the behaviors will converted to an unpacked hkx file.
Open the desired converted behavior file in a text editor and near the top of the file there will be a Havok object called 'hkbBehaviorGraphStringData'. Scroll down until you find this line ''. Just increase the number of elements here.
Then scroll to the bottom of this list of variables and add your custom variable. You need to add your variables to the bottom of this list because all variables are referenced in the file by their index in this list so putting your variables anywhere else will alter the indices, breaking everything.
The next object should be called 'hkbVariableValueSet' so scroll down until you find this line ''. Increase the number of elements here and add the initial value for your variable at the bottom of this list (initialize it to 1).
The last object to find will be 'hkbBehaviorGraphData' and again find the line ''. Increase the number of elements here and add the type of your variable at the bottom of this list.
Then find the hkbClipGenerator class referencing the animation "MT_GetUpFromFront.hkx". This object will have the following line: null change the 'null' value to '#6000'. Then above this object add the following:
playbackSpeed 230 -1 BINDING_TYPE_VARIABLE -1
Note that the object number is '#6000' and 'variableIndex' field is the index into the list of animation variables. So if the total number of animation variables is 231, with your new variable the last one, then the index of your new variable is 230.
Then find the hkbClipGenerator class referencing the animation "Mt_GetUpFromBack.hkx". This object will have the following line: null change the 'null' value to '#6000'.
Now both of those animations will have their playback speed controlled by your new animation variable.
Save your file and to repack it use the hkxcmd command 'hkxcmd convert behaviors -f SAVE_CONCISE'. Your altered file should be named 0_master-out-out (rename it to 0_master) and you can the just create a meshes\actors\character\behaviors directory in your Skyrim data directory and put your altered behavior file in the behaviors sub-directory.