Is there actually a difference?
Yes, there is a difference: That is for sure. It would usually be unnatural for a language to have multiple words or phrases to express the exact same idea if there were absolutely no difference among them at least in one aspect.
(What I do not know as an average, run-of-the-mill native Japanese-speaker, however, is whether or not you would be required to be aware of the difference as an N2-level Japanese-learner.)
On the native level, 「たら」 is generally regarded as more informal and/or colloquial than 「れば」; therefore, this difference will be retained when forming phrases and sentences containing 「れば」 or 「たら」.
Thus, 「～にしたら」 is more informal than「～にすれば」, and 「～にしてみたら」 than 「～にしてみれば」.
As a matter of fact, this difference I speak of can be clearly seen in the three example sentences that you yourself have listed (unless this is happening by sheer chance without the author's intention). The first sentence uses 「～にしたら」 with the fairly informal and colloquial phrase 「心配なんだよ」. (I hope you could tell 「なんだよ」 sounds pretty colloquial.)
The second and third sentences use 「れば」 with the far less informal 「～と思う」 and 「かもしれない」, respectively.
Are they interchangeable?
Only to an extent, yes. You would need to know that native speakers would rarely fail to notice the awkwardness of a sentence in which one randomly uses words and phrases of different formality levels.
My advice is always: "If you changed one word in a sentence, you might also need to change a couple of more."