When writing a speech introduction for high school seniors concerning the process of applying to colleges, what are the best ways that you can grab their attention and be more effective? Would the use of statistics be too complicated or boring?

Unfortunately, there is no single answer. I'll review the reason why, and some general principles, to help you start your speech.
The reason why there is no single answer is that there is no single audience of high school seniors. Imagine two different high schools. One is a well-funded magnet school where 90+% of the students go to college. The other is poorly funded, and is one of many schools in the United States where only 60% of the students graduate high school, let alone go on to college. Those two audiences need very different speeches and very different appeals.
Start your process by knowing your audience. In the first example, students assume they'll pass through the application process smoothly, and you mainly need to guide them in the best ways and away from dangerous mistakes. In the second, students likely assume college isn't for them at all. For that first audience, yes, statistics could be useful, if they are simple and focused. You want to grab and focus their attention. So, something like knowing which colleges students at the school apply to is essential, as well as what worked for them and why. You could try something like like this:

There are 450 students in this auditorium. If you're like last year's class, 320 of you will apply to University X. And half of you will get rejected. Half. That number can go down if you do the following when you start your college application process...

The second audience would likely need a less stark challenge, and would probably benefit from something encouraging. I would likely use a story about successful students from their high school who attended and did well in college to show them it is possible. I'd introduce the process of applying for college later.
https://www.dosomething.org/us/facts/11-facts-about-high-school-dropout-rates