[MichaelLeong]

How much difference can I expect if I upgrade my $15 earbuds to a $75 earbuds/headphones?

 

[FrequencyBlue]

depend on how well your ears can differentiate
depend on your taste of sound signature
depend on your current earphones and the earphones/headphones you got your eyes on.
and etc...
 
 
you can only answer your question if you actually go out and audition the phones by yourself
but usually there's away the difference, even if you have the best $15 phones and you try the worst $75 phones ever made

 

[Cakensaur]

really, Diminishing returns hits at about $150 for headphones,
so assuming you buy smart within these price ranges, you will notice a difference between $15 and 30, $100 and $120 and so on
 
Its MOSTLY the headphone you buy based on predetermined factors such as music taste which make a headphone worth it, 
there are a bunch of basshead, treble head and mid centric phones in this price range though... so whatever you like there will be an option
 
So assuming that YOU know what you like, there will be a difference.
 
Hope i've helped,
 
Cakensaur.

 

[Avincent52]

My experience. 
After I lost my Etymotics a couple years ago, I used generic IEMs for a while. $15-$25 models I'd get at Target, etc. 

Heading out on a trip, I splurged on Etymotic MC-5s for $55. 
Huge, huge upgrade.
Much better resolution, more detail, much better bass (which is not an Ety strong suit), amazing isolation.
These things only became apparent
a) once I broke them in for a while (30 hours?)
b) once I found just the right tips (large 3 piece silicone)

I was so jazzed by the MC5s that I decided to upgrade to the HF-5s which you can buy at B & H for $100. 
Another huge upgrade.
Even more detail, better sound staging, really amazing resolution. 
But only after a break in, and the right tips which happened to be the ones from the MC5. 
(the HF-5s were just a little smaller.)
 
The difference between the cheapies and the MC-5, anyone can hear. Some people might not care, might find the detail annoying or distracting, but it's really obvious. They also might not want to make the effort to get the right tip/seal--there's a trick to putting them in right which you can learn from an Etymotic video-- or even care for something sitting that deep into their ear canal. 
 
The difference between the MC5 and the HF-5 is more audiophile stuff. Some might even prefer the MC5, but the difference is pretty striking.

I'm using these directly into an Iphone 5 as well as a Macbook pro, both with and without an Audioquest Dragonfly DAC.
 
I do have a problem with spending a lot on IEMs because they're prone to getting lost or broken. (I've had a pair of Grado full size headphones for 20 years and a pair of Yamahas for longer but I've got a graveyard of IEMs) But for $100 the HF-5s are a real bargain, and if you're posting on this board, Im assuming you'd at least appreciate them.
 
Falling in love, that's a different matter.