Kinda big, yes. If you want you should do some research regarding the DVMT-prealloc setting for your particular Dell BIOS . Some details on how to do it seem to be specific for each system and each BIOS version. Only then you would figure out if that's the problem. You'll probably need Windows for this.
On the other hand, the real 13" MacBook pro has 1440x900 scaled resolution, the 13" MacBook air has this native resolution too, and maybe that's how big it is supposed to look for the user interface. So, this should be an usable working scaling resolution for you while you take your time to sort it out if this is such a big problem.