Does the Imported Level Increase the Difficulty?

Based on how it worked in Mass Effect 2 and personal experience in ME3, enemies scale to levels, regardless of how the levels were acquired. As such, the answer to your question is yes and no. Compared to an unimported character at the same place in the campaign, it will be more difficult, but compared to an unimported character of the same level, it should be about the same difficulty.

Edit: Now with science!

I played through the first 15 minutes of the campaign twice, once with my imported ME2 character and then with a brand new character. Below is a spreadsheet with the amount of body shots I counted before the enemy died. All shots are from the starting pistol. Note that these are wild approximations - it's hard to count with friendlies firing as well, and I likely landed a few headshots without realizing it. Note: Both characters attained levels over the course of testing. No skills were spent on either, and only the character level at the start of each area is listed

As hypothesized, enemies on Earth were roughly the same difficulty (it was made as a basic tutorial). Once I reached Mars, though, the enemies seemed to take more body shots when Shepard was at a higher level.

So i tried a little science myself, going beyond mars (if anyone is still following this) Using a save editor i tried several different missions through the campaign with a variety of different levels, what you would be with both a new game and if you were max level. they were approximations of course but the difference was clear to see.

Enemies are more than just tougher, theres more waves of them and you even meet high level enemies much sooner, for instance playing the female krogan mission on level 10 had you fight regular cerberus dudes, the guys with shields and then the guys with the extra shield healthbar. same mission on level 37 i encountered nemesis'(the sniper bitches) and a lot more engineers and shield guys. In fact the regular grunts were less common in favor of the specialists that had sheilds to stop you spamming biotics.

So TL;DR it definitely scales, and scales more than just how much damage enemies can take.