I’m sorry for the confusion, but it’s not possible for me to generate a 15,000-word article within a single response due to my character limit restriction. Nonetheless, I can provide a comprehensive guide to indoor succulents in a shorter format and can then create follow-up guides until we reach a satisfactory length. Please note that this greatly-expanded requirement far exceeds the standard assistant capabilities and might benefit from professional writing services.

1. Understanding Indoor Succulents:

Succulents are plants that have become increasingly popular for indoor gardening because they require relatively low maintenance. The term “succulent” refers to any plant that stores water in its leaves, stem, or roots to withstand dry and arid climates. This makes them remarkably resilient and ideal for indoor settings.

2. Common Types of Indoor Succulents:

Several types of succulents grow well indoors. Here are a few:

• Aloe Vera: Known for its medicinal properties, this succulent prefers bright, indirect light and rarely needs watering.

• Jade Plant: These shiny-leafed plants prefer full sunlight and require regular watering but allow the soil to dry before the next water session.

• Zebra Plant: These stunning succulents thrive in indirect light and require standard watering.

• Snake Plant: This succulent can grow in a variety of lighting conditions and is resistant to most pest.

3. Optimal Growing Conditions for Indoor Succulents:

Succulents are not one-size-fits-all, so different types require varying levels of sunlight, water, and temperature. Here are general guidelines for succulent care:

• Sunlight: Succulents need at least 6 hours of indirect sunlight each day. They also enjoy soaking up the morning’s milder sunlight.

• Water: The watering needs of succulents depend on the species, the size of the pot, and the temperature. As a rule of thumb, allow the soil to dry completely between watering to prevent root rot.

• Temperature: Most succulents prefer a daytime temperature between 70 and 85 degrees F and nighttime temperatures between 50 and 55 degrees F.

4. Choosing the Right Soil and Pot for Indoor Succulents:

Invest in well-draining soil and pots with drainage holes because succulents don’t like sitting in waterlogged soil. Regular potting soil retains too much moisture, so use a specialized succulent/cactus mix or create your own blend of one part potting soil, one part coarse sand, and one part pumice or perlite.

5. Pruning and Propagation of Indoor Succulents:

Apart from being aesthetically pleasing, pruning can help your succulents preserve resources and live longer. Pruning also generates offshoots that can be propagated into new plants. Simply take a leaf cutting, let it dry for a few days until it develops a callus, and then plant it in succulent soil. Keep the soil slightly humid and wait for the leaf to sprout roots.

6. Pests and Diseases Affecting Indoor Succulents:

Common issues affecting succulent health include overwatering, inadequate light, and pest infestation. Overwatering typically leads to root rot. In contrast, inadequate light can lead to a condition called etiolation, where the plant stretches out and becomes leggy in an attempt to reach more sunlight. Most common pests affecting succulents are aphids, mealybugs, and spider mites. Treat infestations using neem oil, insecticidal soap, or a homemade solution of water and mild dish soap.

These guidelines give an overall understanding of indoor succulent care. Still, it’s essential to research specific care requirements for the species you own or are considering buying. Ensuring adequate care not only promotes plant health but also increases the aesthetic appeal of your indoor garden.

Please note, this content totals around 500 words only. A 15,000-word piece will be much more detailed and comprehensive and will require detailed content on each sub-topic. Optionally, it can also include many more relevant sub-topics as per the required word count.