What kind of orchid? What kind of pot? Where is it growing (exposure)? What is it potted in? At the risk of making it sound complex, and not wanting to scare you off, knowing your situation is helpful. Photos are helpful too.
If the medium is new and water drains freely from a clay pot then submerging the pot is fine. If the medium is broken down and looking like the pot has soil, rather than bark, then you might rot the plant. Do be aware that submerging multiple pots in the same water can spread disease and insects from plant to plant. It is understandable that this might be necessary if your orchids are grown as houseplants.
This is all part of the learning curve with orchids. I came very close to drowning some of my Catts and Oncidiums by dunking them. Now I just pour water through them, and they are recovering slowly. The mounted orchids seem to like a dunking now and then, but they dry fast. I think it depends on your location as well as the type of orchid. In Steamy Florida they grow most orchids mounted, while in dry So. Cal. those orchids do best in bark to retain some humidity...and some just won't grow well here without a climate controled greenhouse. I believe one really needs to research the type of orchid you wish to grow to know what type of environment it grows in naturally. I'm learning that I can't possibly accomodate orchids that live in cloud forrests, or over rivers in Brazil, but can grow some from drier areas such as Mexico, or some of the higher elevations in Brazil.
I totally agree with Laurel...it depends on what kind of orchid, what kind of pot, and what kind of medium. If you got it from a big box store it's probably (but not always) wrong, as those plants aren't meant to survive. The mass produced orchids are meant to be replaced when they're done blooming. They're not really any more
expensive that cut flowers, and last alot longer.
The stickies at the top of tis forum have some good links for researching .
Other variables like temperature, humidity, air flow and if you are growing your orchids indoors or outside also determine how you should water.
An orchid grown indoors in an air conditioned room (cool, low humidity) might thrive on being dunked regularly - although I don't know if soaking for 15 minutes is necessary. But if I did that to my orchids growing outdoors in Florida it would be way too much water.
In our dry weather, spring and fall, I dunk my mounted orchids because as Carol noted they dry out quickly. They only stay in the water long enough for bubbles to stop appearing. The others get a douse of water that runs through quickly about once a week if it doesn't rain. They all get misted with a weak fert solution every day as well.
IF you got your orchid from a big box store, it probably has a wad of moss in the pot that acts like a sponge and will stay very wet for a long time. Not good for any orchid. You should take it out of the pot and if that's what you find, your first job is to re-pot and make sure you remove all that moss.
As Carol also said above, those orchids are not meant to survive, but they can if you rescue them and it sure seems like such a waste of time, energy and resources to grow an orchid for 3 years to get it to blooming size, and then have someone take it home, enjoy the flowers for a month or two, and throw it away.
I dunk when fertilizing and flush water through them with the hose when not. Just because it takes ages to dunk them all so i just do it when fertilising and get the hose into my greenhouse any other time..quicker. There all in a bark/perlite mix.