Color photography existed far before 1915! Here's a photograph from 1877 by Louis Arthur Ducos du Hauron of the town of Agen. Here's an excellent one from 1911 of Mohammed Alim Khan taken by Sergey Prokudin-Gorsky.

Both of these were done through the three-color method in a different way, but each involved taking three separate photographs. Louis used a carbon printing method in which he used a thin layer of gelatin and carbon-based pigment that would block certain colors of light as it passed through, with the negatives being transferred to their final sheet and overlapping to create a crude color image. Sergey took three black & white photographs with a different filter over the lens each time (blue, green, and red) and then projected the three negatives through filters onto a screen, creating the gorgeous and perfectly realistic image you see there. The problem was getting an image like that onto a positive, rather than combining images on a projector.

Skipping past most of the other experimental history, color photography didn't become a major commercial thing until 1935 when Kodak introduced Kodachrome film. Prior color technology generally used an additive process for color, combining red, green, and blue images to create a final color picture, but this lost clarity and allowed the individual RGB elements to become visible when enlarged too far and needed very bright lamps to project the image cleanly. Kodachrome used a subtractive process, with a multi-layered film where each layer acted as a red, green, or blue color filter. By blocking the other colors from reaching lower layers, a special development process could give you a clean and richly colored image.

After a lot of tweaking to figure out the chemical process and the methods needed to perfect the film, Kodachrome allowed for viable color photography by the average person. However, it would take decades for it to be improved to the point where it was common. Color film was less sensitive to light than black & white, making it harder to use indoors without setting up powerful lights or attaching a disposable flashbulb to better illuminate the subject. The more complicated developing with the multi-layered film was more difficult and consequently more expensive than black & white development (which can easily be done in a home darkroom by an amateur), driving up the cost of color film. For the average consumer, cheap black & white film was used for everyday photography and expensive color film was saved for special occasions like vacations.

It would take until the 1970s for technology to improve enough that color film's price was competitive with black & white, film sensitivity had improved, and electronic flash units instead of pyrotechnic bulbs allowed even small cameras to mount powerful flash units in case your film was still too dull. Black & white finally disappeared except for artistic purposes...just in time for digital cameras to start taking over!