Hi @denisef -
I have wondered the same thing. BTW I think you mean decreasing (not increasing) the gastric emptying time. I am hoping that someone responds who can share their experience with probiotics.
In the meantime, here is one study with some strange results for age brackets versus BMI brackets. Not sure about the publication quality.
Evaluation of multi-strain Lactobacillus capsule on gastric emptying function b emptying function by Tc-99m scintigraphy in a crossover placebo-controlled clinical trial (Journal of Food and Drug Analysis, 2012):
"In the 20-40 age group, the half times of gastric emptying (GEt1/2) for baseline, placebo, and Lactobacillus regimen periods were 73.0 ± 16.0, 85.7 ± 10.5 and 87.8 ± 10.0 min, respectively, while those in the 41-60 age group were 79.1 ± 23.9, 70.9 ± 33.1 and 68.4 ± 15.2 min, respectively."
"The GEt1/2 of the 20-40 year-old subjects who took the lactobacillus increased. This indicated that the lactobacillus regimen does not promote the effect of gastric emptying. Meanwhile, the GEt1/2 of the 41-60 year-old subjects who took the lactobacillus decreased. This indicated that the lactic acid bacteria regimen does endorse the effect of gastric emptying."
"In this study, BMI between 20 to 25 were assigned as the BMI normal group, while the others were assigned as the BMI abnormal group. The results showed that after the subjects with normal BMI took lactobacillus, their gastric emptying time did not decrease. However, after the subjects with abnormal BMI took lactobacillus, their gastric emptying time decreased. Therefore, for people with abnormal BMI, taking lactobacillus might improve their gastric emptying function."
Also, here is another excerpt:
GoodRx Health: Some people may wonder if probiotics help with gastroparesis. The science isn’t clear on whether they’re helpful. One study found that probiotics might be helpful for improving delayed stomach emptying. But larger studies are needed to confirm these benefits. Plus, some experts report that taking probiotics might worsen bloating caused gastroparesis.

Hope someone can share their experience!