Modifying your .Target.cs file with these options can help make the pdb size smaller.
WindowsPlatform.PdbPageSize = 8192; // allows for PDBs greater than 4gb
WindowsPlatform.bStripUnreferencedSymbols = true;
WindowsPlatform.bMergeIdenticalCOMDATs = true; // we need the pdb space and have to pay the extra link time cost
bDisableDebugInfoForGeneratedCode = true;
// make sure PDBs are always regenerated.
bSupportEditAndContinue = false;
bAdaptiveUnityEnablesEditAndContinue = false;
bUseIncrementalLinking = false;
Another option could be to use:
bUsePDBFiles = false;
which puts the debug information in the .obj file. For more information on what these are doing you can take a look at:
Which is a great microsoft blog post on the topic