A compound-complex sentence actually has
two (or more) equal clauses and
one (or more) dependent clause. In this case, there's only one independent clause and one dependent, therefore makes it a complex sentence.
A complex sentence has two or more clauses, where there is one subordinate clause. A subordinating conjunction may be a marker of a subordinate clause and for this example, it would be "If" just like how you stated
It is a complex sentence because one clause depends on the other clause to make sense or be fulfilled.
I have separated the two clauses in brackets.
"[If you are thinking about starting a business], [you might benefit from our free seminars and online visits]"
(Dependent) (Independent)If "If you are thinking about starting a business" was standing alone for sentence, it would feel unfinished therefore depends on another clause for it to be complete.
I hope this makes sense!