[MasterfulButch]

Personally I'd be cautious about trying to differentiate the two by comparison with one another because when you do it's natural to end up positioning one as better than the other. I believe there's a considerable scope to both as well as an area where they overlap. Equally, I think they are both a valuable part of our experience and when society holds love in greater esteem it can leave the person with a crush feeling invalidated. It doesn't help that crushes are often attributed to feckless youth which can leave a person with very real emotions feeling patronised and isolated.

When talking to the fifteen year old, I'd approach it from a different angle. Instead of following the cultural narrative for defining the two, I'd instead say that they should focus on how it makes them feel.

Is it exciting, frustrating or both?
Does the thought of a future with that person feel like a daydream?
Do they feel valued by the other person as the individual they are without the need for change?
How do they feel about themselves when they're with that person? Do they like themselves more, less or the same?
Does it feel like they are empowered in the situation or more at the mercy of the actions of the other person?
Do they have an urge to justify the existence or significance of what they are feeling either to themselves or to others?

From my experience I have felt both sides to all the above for relationships I have defined for myself as crushes and those as love. I think learning to accurately quantify and label something is a lot less important than it is to prioritise what it means to you. If you put your focus on how it makes you feel then you can act on what is the truth for yourself which is a much more empowering position to be in.

As a side note, I'm only just starting to see some of the cultural messaging I've picked up over my life so far and it's made me realise how insidious this can be. I would always be cautious about saying that true love has challenges or relationships take work. While I agree that life can be challenging and sometimes that takes the form of situations partners find themselves in, I don't feel like my partner is the challenge. It feels like we're in it together, united as we face the external circumstance or difficult interaction between us, mutually prioritising love and respect for the other as we go. The point being that when people talk about relationships being hard, it can set up the message in your mind that if you want a good relationship you have to stick at something that may actually be damaging for you. This is why I would get the fifteen year old focused on how it feels to them rather that continuing to define things by external standards. It's their experience that matters, not anybody else's.