There are several questions here. I'd like to address two of them.
- Does Exodus 15:11 hint at the possibility of existence of lesser gods?
The answer here depends on whether the question "who is like you among the gods" is taken literally or as a rhetorical device meant to emphasis that other supposed deities are not real. But it is probable that the early Israelites did believe the other gods were real, and continued to do so for centuries.
In Exodus 18:11, Moses' father-in-law Jethro, a priest of Midian, declares "Now I know that the LORD is greater than all gods." This attitude may also have been typical of the Israelites themselves. The other gods are real, but Yahweh is the greatest. Also, even though the OP's verse presents itself as coming from the time before the Torah was given, another much later OT verse uses this same question, namely Psalm 86:8.
The technical term for this attitude is called either henotheism or monolatry. The person or nation believes there are many gods but he is to worship only his nation's deity exclusively. This may be the idea behind the second commandment:
7 You shall not have other gods beside me... For I, the Lord, your
God, am a jealous God... (Dt. 5:7-9)
Note that this core scripture does not deny the existence of other gods; rather it describes Yahweh as commanding that he alone be worshiped. Perhaps the clearest Biblical expression of the principle of henotheism is seen in Dt. 32, where Yahweh himself is seemingly subservient to a deity called the Most High:
Ask your father, he will inform you,
your elders, they will tell you: 8 When the Most High allotted each nation its heritage,
when he separated out human beings, He set up the boundaries of the peoples
after the number of the divine beings; 9 But the Lord’s portion was his people;
his allotted share was Jacob.
Here the Supreme Deity is "the Most High" (ʿelyôn), and it he who apportions various peoples to the other divine beings. Yahweh's portion is "his people... Jacob." Other translations prefer "sons of Israel" to "divine beings" here, but in either case there is a deity called 'Elyon - the the Most High God - who gives Jacob's descendants to Yahweh.
- Is it possible that some Israelites worshipped lesser gods apart from the True God Yahweh?
Yes. They were not supposed to, because according to the Ten Commandments they were allowed to worship the LORD (Yahweh) alone. But they definitely hedged their bets on occasion, or even switched allegiances; and the Bible often describes them as being punished for doing so.
So, whether the OP's verse intentionally hints at the real existence of other gods or not is debatable. There does indeed seem to have been a time in Israelite history when the real existence of other deities was presumed. However, the Israelites were not allowed to worship any god other than the LORD.