Grumble if you like, but terse-and-clear is the mark of good writing. Whether or not you think a sentence is too short, in order to write well, it probably isn't too short at all.
Read that 15-word sentence again. You can cut words. Whether implies or not. At all is redundant and you can cut in order. I'd suggest you make the sentence read this way: If you think a sentence is too short, it probably isn't.
When I first started to write, the late Charlie Shedd taught, "Never make a sentence longer than 15 words." His words were a bit arbitrary, but in those days 50 words wasn't too long a sentence. Yet vigilantly limited to no more than 15 makes choppy writing.
Here's how I say it: "Let your sentences average no more than 20 words." Good writing doesn't demand a word limit on a sentence. Take as long as you need to express a thought. Afterward, go back and ask if you can eliminate words or perhaps make a long sentence into two.
If you write succinctly and clearly, you're one rung higher on the good-writer ladder. You can figure out the antithesis of that statement. Antithesis is a good word, but it may be beyond the vocabulary of some readers. Why not say the opposite? That's another tip.
Good writers cut ruthlessly.